Gas-producing compositions of smokeless powder and metal compound inhibitors



3,009,796 GAS-PRODUCING COMPOSITIONS LESS POWDER AND METAL COMPOUND IN-HIBITORS Ralph F. Preckel, Frostburg, Md., assignor, by mesneassignments, to the United States of America as represented by theSecretary of the Navy No Drawing. Filed Mar. 8, 1.951, Ser. No. 214,629.1 Claim. (Cl. 52-5) The present application is a continuation-in-partof my copending application entitled, Gas-Producing Charge, Serial No.102,427, filed June 30, 1949, now abandoned, and as'in the case of saidpreviously filed application, the present invention relates to smokelesspowders and more particularly to smokeless powders having ballisticcharacteristics peculiarily desirable for application in jet actuateddevices.

'It is well known that there is a definite and direct relationshipbetween the pressure at which a smokeless powder propellant burns andits burning rate. This relationship may be mathematically expressed asr=cp or as log r=n log P+log c, where r is the burning rate, P is thepressure at which the burning rate is measured, and c and n areconstants characteristic of a given propellant. Thus, when a plot of logr against log P is made for the conventional propellant, a straight lineof slope n is ob tained showing an increase in burning rate for eachincrease in pressure. Such a relationship is not disadvantageous in theconventional propellant, and in fact is used to advantage in progressivepowders where it is highly desirable to generate increased pressuresafter the projectile or shot charge has begun to move-along the barrel.However, this relationship presents a serious problem in formulation ofpropellants for jet-actuated devices, since once the desired operatingpressure is reach, totally different considerations obtain.

It is highly desirable, once the operating pressure of a 'jet-actuateddevice is reached, that the pressure generated by the burning propellantbe maintained as nearly constant as possible. Accordingly, if thisresult is to be attained, the slope n of the line representing thepressureburning rate relationshipv of the particular propellant shouldpreferably approach zero in the zone of useful rocket pressure. In theprior art rocket powders, in all of 'which the slope n has a value of0.7 or over, any fracturing or slivering'of the propellant charge leadsto a pressure build-up because of an increase in linear burning rateresulting from the increase in pressure due to the increase in burningsurface." The higher then value of the particular powders, the higherwill be the pressure rise encountered. Therefore, the results of such afracturing or slivering vary from a highly undesirable thrustfluctuation, with consequent aberration in ballistics, to actual failureof the jet device if, as with a propellant of high It value, thepressure build-up is excessive. Even unusual roughness of the chargecauses serious changes in burning pressure and burning rate in thepresently available rocket propellants, with the result that errors of1% in the nozzle diameter have been found to buildup to an aberrationof'- 5 or more in ballistics. Consequently, with the propellant's nowavailable, there is 'very little allowable tolerance in manufacture ofcharges and nozzles for jet devices. A propellant having a very low nvalue within therange of useful rocket pressures, however, would allowfor considerable tolerances without appreciabledeviation from thespecified ballistics, and accordingly any decrease in ;n value wouldaccordingly enhance the value of a particular propellant.

' A second serious problem confronting producers of propellants forjet-actuated devices is the diminution of the temperature coefiicient ofequilibrium pressure at the OF SMOKE- 3,009,796 Patented Nov. 21, 1961desired operating pressure or pressure range. The temperaturecoefficient of equilibrium pressure is a measure of the pressurevariation to be expected from a given propellant on account oftemperature variation alone. It is obtained by firing identical samplesof propellant under identical conditions except for changes intemperature and pressure. The coeificient may be expressed as peraturerange ordinarily specified for such devices in field use.

Since existing propellants generally have temperature coeificients ofequilibrium pressure of about 0.8% C. or more, service pressure maychange by 100% or more in going from the lowest expected temperature(about 55 C.) to the highest expected temperature (about C.). It istherefore highly desirable to lower the temperature coefficient ofequilibrium pressure below' that of existing rocket propellants andthereby hold variations in service pressure due to temperature changesto a minimum. If the coefiicient could be lowered from 0.8%/ C. to 0.4%/C. or less, service pressure variation would be diminished by at leastone half, and similarly any lowering of this temperature coefiicientwould correspondingly enhance the value of the propellant.

As a result of the advantages set. .forth above fora propellant having alow n value and/or a low temperature coeificient of equilibriumpressure, either or both of these two ballistic characteristics wouldallow for important economies in the inert weight of jet actuateddevices. This is clearly seen if the equation is examined which relatesthe ratio between the mass of propellant (m) and the mass of the jetdevice without propellant (M), the gas velocity of the burningpropellant (V), and the highest theoretically obtainable velocity of thejet device (V as follows:

V lOgm With propellants now available, the highest ratio of m/M has beenabout 1, wheremass of propellantand mass of jet device are about equal.If it is possible, by use of a new propellant which does not build upexcessive pressures, to decrease M by 10% and increase the amount ofpropellant to give the same total initial weight, V would be increasedby a factor 1.1 gic (1+ or about 1.15. This would beat 15% improvement.

Therefore, an object of the present invention is the production ofpropellants for jet-actuated devices which are characterized by lowburning rate-pressure relationships throughout a wide pressure regionwithin the range of useful rocket pressures.

A further object of this invention is the production of propellants forjet-actuated devices which are characterized by low temperaturecoefficients of equilibrium pressure, thus minimizing variations inservice pressure due to temperature.

The previously mentioned copending application is directed to smokelesspowder propellant explosives which haveincorporated therein atleast onematerial selected from the group consisting of lead and compounds oflead,

and which have heats of explosion of not more than about 900 caloriesper gram. As there described the addition of these materials to saidpropellants causes a substantial reduction in the n value and thetemperature coefiicient of tion by uniformly incorporating therein minoramountsof niany other metals and compounds of metals, as morespecificaly set out hereinbelow, provided these compositions ofpropellant and modifier have heats of explosion of not more than about900calories per gram. As pointed out in detail in the earliermentionedapplicationwith specific reference to the lead and compounds of leadmoditiers, the smokeless powders to which these ballistic'modi- 'fiersare added may be either single or multiple base a powders. Ifthe-smokeless powder to which one or more of the ballistic modifiers isadded is a single-base powder, it should preferably comprise fromf85 to95% nitrocellu- V lose and from to plasticizer. if the propellantused ina multiple-'base-formula, it shouldpreferably comprise from 40 to 85%nitrocellulose, from 10 to of an explosive liquid ester, and from 5 to30% of a substantially nonvolatile nonexplosive plasticizer. In anyformulation, however, his critical that the heat of explosionfof theadditive system be not greaterthan about900 calories per gram. -For, asshown in said previous application, Where formulations have heats ofexplosion in excessof said i amount, the additiveballistic modifierslose a considerable amount of their effectiveness in. suppressing the nvalue and the temperature coeificient of equilibrium pressure in 7 caseswhere the latter suppression is eifected. As further pointed out in saidapplication, the heats of explosion of 'ValiOfiS formulations can bereadily calculated byione skilled in the art to determine whether theformulations are isuita-ble for the purposes of the; present invention.Smokeless powder propellants prepared in accordance various operableadditives maybe employed without ad- .versely arfectingithe ballisticsofthe gas produci'ng comwhen indicated modifiers-are added thereto 1namounts stated.

' Modifier Temp; Pressure coef. of 7 Y Heat of Low-- regionoi pressureEx. Amt, explosion est n lowest 11. in region Typo pereaL/g. p.s.i. oflowest -centn per- 7 centl O;

0.7 0. 0.5 0.3 1,4003;000 0. 2.0 0.2 l,'500'3,300 0. 4.0 0.2 .l,4003,6000. 1.0 0.3 1, 000-2, 000v 0. 1.0 0.2 1,300-13800 1 0. 1.0 0.3' 2, 000-2,400, I 0. 1.0. a 0-2 Lane-2,400. j Q7 0.5 0.3 Loco-2,350 q 0. 1.0 0.3-LOGO-2,500 V 0. 2.0 0.2 1,3002,000 .0. 1.0 0.7; l,3002,000 .0.

1 0 695 0 3 1,?500-1'650 0.4 1 0 695 0 3 l,7502,900 0'3 1 0 695 g 0 600-2000 1.2 1 0 695 0 5 -1,3002,000 0.7 1 0 695 0 4 LEGO-2,400 0.6; 1 0695" 04 1,300-2200 0.3 1 0 695 0 4 'l,5002,250- 0.9

(subcarr g V bon'ate).- j 20-. Arr'rgiorphous. 1.0 695 0.4 2500 .4,0000. 21;; Mo p'wd.. .i. 1.0 695' 0.4 LOGO-2,600 0. 22 U505 (uraib, 1.0 6950.4; 6201,350 0.

, ium oxide). v 23-; BaCO;4 1.0 695 0.4 1,100'2,000 0. 24 1.0 695 0. 4'1, 400-1, 900 0. 1.0 695 0.5 1,200%2,700 .0. 1. 0 695 0. 5' l, 100 1,900 0. 1.0 695 0.5 l,3002,750 0. 1.0 695 0.5 100 500 l. 1.0 -695' 0:61,500 2;500 0. l. 0 695 OI 5 1, 2502, 200 0. g r 1.0 :695 0.5 v.',60,0-2',,0oo 0. a 0. 5 700 0. 5 1350 3, 100v 0. 33.. TiOz 1.0 "695'0. 5' 1,000-4,0 00 l. 34.. Spwd- .1.0 695 0. 5 300- 890 1. 35.- Diutyltin "1.0 680 0.5,- 200- 600 0. r -diacetate./ I i,

positions -of the invention, however, it is preferred to em ploy onlys'ufiicient amounts of additives to effect the desired modification inballistics. In most cases it has been weight of the smokeless powderemployed, is ample.

fouricl that 2% of the various additives, based on the Having nowgenerally described the invention, the following table presents a'plurality of examples' of ballistic modifiers which when employediii-accordance with the present invention provide substantial decreasesin the n value of smokeless powder propellant explosives, and, as

e'quilibriuni'.pressure.' This tableindicates the hea t of explosion,lowest 71, pressure region of lowest n,and temperature c'oefiici'ent ofpressure in region of lowest n for a standard rocketpropellantcomposition having the follow a binitrotoluene will be noted,some instances alsofeffect a substantial reduction in the prop'ellantstemperaturecoefiicient of 'From the examples' given in the fore goingtable, iit

is apparent that although all of the ballistic modifiers there disclosedare operable in lowering -n value, range of variations in'geifectonnvalue and ontemperaofapartieular modifier employed. These facts; providefor. considerable flexibility in employing the teachings of the presentinvention, enabling a wide choice of modifiers and amounts thereof basedp11 economic considerations as well as theballistics desired foraparticular application I of the invent-ion. By reference to theforegoing table,

one skilled in. the art can readily determine the nature and amount Iofxmodifier appropriate [for accomplishing the desired ballisticmodifications Manyexamples of propellant powder formulationsfoundtorespondas indicated to additions of .small percentages of said modifiershave been disclosed in my copending lapplication above- I identified,and furthermore, said application 'clearly dis-" closes the generalprinciples and criteriafor: determining whethenornot .a particularpropellant powder respond inrthe manner indicatedin the; f regoingdescription of the present invention. a

r The foregoing -.spec ific examples [of modifiers amounts of modifiersemployed, and'theparticula'r propel lantpowder formulation indicated arepresented merely by way of example, to clearly indicate the nature andsignificance of the resent invemim. Msaificatnns'ef these details willbe apparent re mor skilled in the v art, and such modifications as arethe spirit and scope of the present invention as defined by the appendedclaim are within the contemplation of the present patent.

What is claimed is: i

The method of diminishing the n value and temperature coeflicient ofequilibrium pressure of a double base rocket propellant in a pressureregion suitable for operation of a rocket device, said propellantcomprising 40 85% nitrocellulose and 10-35% nitroglycerine and having aheat of explosion not to exceed 900 calories per gram, comprisinguniformly dispersing throughout said composition a ballistic modifierselected from the group consisting of silver and silver oxide inquantities adequate to obtain the desired reduction in said It value andtemperature coeflicient but not to exceed 10% by weight of saidpropellant, wherein the n value of said propellant is the slope of theplot of the log of the burning rate (r) against the log of the pressure(p) at which the burning 6 rate is measured, and the temperaturecoefiici'ent is equal to AP/gTAt wherein AP is the diflerence inpressures due to the temperatures change Ar and 17 is the meanof thepressures.

References Cited in the file of this patent UNITED STATES PATENTS1,336,463 Henning Apr. 13, 1920 1,357,865 Henning Nov. 2, 1920 1,943,421Burns et a1 Jan. 16, 1934 1,963,116 Burns et a1. June 19, 1934 2,038,700Woodbridge Apr. 28, 1936 2,131,352 Marsh Sept. 27, 1938 15 2,344,840Watt et a1. Mar. 21, 1944 FOREIGN PATENTS 621,685 Great Britain Apr. 14,1949

